Some people report sensing a flowery smell in some places or situations in which there are no flowers present. Those sensations are sometimes related to religious experiences.

There are also claims that the sensation has no scientific explanation.

The fragrance of roses and the
smelling of roses is frequently
mentioned in records of mystical
experiences. How to explain it? I am
not sure if there is a scientific
answer. I haven't seen any, not so
far.
(source Catholic Web: Smelling Roses--What is the meaning? )

Just for measure, olfactory hallucinations (sometimes called phantosmia) are common before certain types of migraine or seizures. If the seizure occurs in the temporal lobe, patients often describe having religious visions. These are both documented medical/neurological phenomena which can be verified.
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Monkey TuesdayApr 19 '11 at 19:01

Those are hallucinations. You can have all sorts of sensual hallucinations: visual, audible, smelly, etc. .
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Bogdan0x400Apr 20 '11 at 13:32

1

Do hallucinations appear more frequently in religious settings? If so, why? If not, do religious people just tend to interpret their perceptions differently? What is the medical explanation for hallucinations?
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ipavlicApr 20 '11 at 13:39

8

Imagining something is a hallucination by itself. Religious people imagine lots of things.
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Bogdan0x400Apr 20 '11 at 13:43

7 [cases, n.d.r.] were direct temporal lobe signs that implied deepened affect, auditory-vestibular experiences (vibrations, hearing one's name called), olfactory auras, perseveration ("forced" thinking), depersonalization, and sense of the personal. Five items involved beliefs about exotic phenomena or philosophical ideas. Only one item was from a control cluster. These results support the hypothesis that mystical or paranormal experiences are associated with transient electrical foci within the temporal lobe of the human brain.

These behaviors and beliefs are related to activation of the amygdala, hippocampus, and temporal lobe, which are responsible for religious, spiritual, and mystical trancelike states, dreaming, astral projection, near-death and out-of-body experiences, and the hallucination of ghosts, demons, angels, and gods. Abraham, Moses, Muhammad, and Jesus Christ, and others who have communed with angels or gods display limbic system hyperactivity, whereas patients report religious hallucinations or out-of-body experiences when limbic structures are stimulated or excessively activated. It is postulated that limbic and temporal lobe structures account for the sexual and violent aspects of religious behavior and also serve as a “transmitter to God,” and that the evolution of these structures made spiritual experience possible.

Another well known cause of olfactory hallucinations is schizophrenia, which is sometimes related to strange or extreme religious behaviour.

Religious Delusions
The subject is preoccupied with false beliefs of a religious nature. Sometimes these exist within the context of a conventional religious system, such as beliefs about the Second Coming, the Antichrist, or possession by the Devil.